The invention relates to a capacitive sensor for length and angle measurement.
Since the coming out of capacitive displacement sensor for large displacement measuring in the seventies of the century, due to its advantages on low power consumption, high integration, small volume, and low cost etc, extensive applications had been achieved rapidly on digital display measuring tools and other length measuring devices. However, because of its lower resolution and measuring precision in comparison with the sensors like the gratings and synchronous inductor etc, therefore a certain limitation occurs in aspects of high precision measurement. While the simplest and most effective method for raising resolution and precision of capacitive displacement sensor is reduction of the spacings between the emitting electrodes 12 of a subsidiary scale and reduction of the spacings among the reflecting electrodes 10 of a main scale simultaneously, as shown in FIG.6. According to arrangement for the prior art""s emitting electrodes 12 of subsidiary scales, in a pitch T of the subsidiary scale, 2N (N is an integer, 2N=8 to be set in the drawing) emitting electrodes transmitting different signals are involved. If the various emitting electrodes 12 in a pitch T are numbered as 1,2,3,4,5,6,7,8 according to the position sequence, there are a plurality of emitting electrodes 12 with a pitches T, and emitting electrodes in each pitch T must have gaps S and a receiving electrode 11 is placed on one side of the emitting electrode. If the spacing t between the emitting electrodes 12 were reduced according to aforesaid form of arrangement, then the gaps between the adjacent emitting electrodes shall be extremely small so its technological difficulty is obvious. Moreover since there is a gap S between the adjacent emitting electrodes 12, therefore discontinuity of signals shall be presented while the reflecting electrode 10 on the main scale traverses two emitting electrodes 12, thereby precision of the sensor is influenced. In the patents (CN87102624) (CN1038421), it was proposed to take out the emitting electrodes on the subsidiary scale originally concentrated in a pitch T respectively, then to dispose them on the same positions of different pitches T separately so that each emitting electrode being broadened, and improving its resolution but not increasing the technological difficulty. But a group of emitting electrodes in this kind of arrangement shall correspond to multiple reflecting electrodes respectively, so that no complete signal can be synthesized on a reflecting electrode. A reflecting electrode must be coupled with a receiver electrode once again to compose a complete synthesized signal. However the variation of capacitance is directly proportional to the square of the distance between both capacitor plates, thus an extremely high parallelism of the main scale and the subsidiary scale is required, otherwise the precision cannot be reached, consequently its application shall be rather difficult. Furthermore, when the reflecting electrode is traversing the overlapping portions of two emitting electrodes, the sensor precision shall also be influenced due to said signal discontinuity.
An object of the invention is to propose an improved capacitive displacement sensor, which can not only improve the resolution and precision of capacitive displacement sensor, meanwhile the fabrication technological difficulty is also not excessively increased, and the applicable function of improved capacitive displacement sensor can be conveniently extended.
The capacitive displacement sensor of the invention comprises a main scale and a subsidiary scale arranged in a relatively mutual movable mode; 2N (N is an integer) emitting electrodes 12 are disposed on the said above subsidiary scale for transmitting different signals, said emitting electrodes 12 being perpendicular to the subsidiary scale and arranged in each pitch T; a receiving electrode 11, said above emitting electrodes 12 and reflecting electrodes 10 opposing the receiving electrode 11 are installed on the said main scale; and an electronic circuit for measuring the relative displacement by means of the coupling capacitance between said above emitting electrodes 12, receiver electrode 11, and reflecting electrodes 10,
wherein, the adjacent emitting electrodes 12 in the same pitch T of the subsidiary scale are arranged on both sides of the receiver electrode 11 respectively, and all the emitting electrodes 12transmitting different signals still are involved in a pitch T, the geometrical gaps of adjacent emitting electrodes 12 along the longitudinal direction of said subsidiary scale being zero, i.e. the neighboring sides between the adjacent emitting electrodes 12 located on a straight line. Corresponding to arrangement of the emitting electrodes 12 in each pitch T, the arrangement sequence of the emitting electrodes 12 in another pitch T separating several pitches with the said above pitch T is alternatively arranged with the aforesaid emitting electrodes 12, and the gap among the neighboring two groups several pitches T.
A plurality of units formed according to the mode of arranging emitting electrodes on both sides of receiver electrode 11 respectively, and the geometric gaps between the adjacent emitting electrodes being zero may be disposed, along subsidiary scale wherein a spacing of several pitches T occurred among the two adjacent pitches, and the arrangement sequences of the emitting electrodes 12 in the two adjacent units are alternatively allocated.
The form of reflecting electrodes 10 of the main scale may be a tumbled letter xe2x80x9cTxe2x80x9d shape relatively to the main scale.
Also, a pitch of the reflecting electrodes 10 may equal a pitch T of the emitting electrodes 12.
The reflecting electrode 11 may be rectangular shape, its length may be integer times of the pitch T of emitting electrodes 12.
Furthermore, both ends of receiver electrode 11 may be T/2 shorter than the both outer ends of emitting electrode 12 respectively.